1. Field of the Invention
The present invention relates to a temperature detecting apparatus or device for image fixing means to be used in an electrostatic recording apparatus.
For example, in the electrophotographic copying machine, a toner image developed from an electrostatic latent image produced on a photo-sensitive layer is transferred to a recording or transfer sheet and subsequently fixed to the sheet by means of heating means such as a pair of rollers containing at least one heating roller.
In the case of the standard recording or transfer sheet, the fixing temperature is usually in the range of 150.degree. C. to 170.degree. C. The range of the fixing temperature can be determined by conditions, for example, such as a recording speed or a thickness of the paper to be used and so forth.
Unless the fixing temperature is maintained at a constant value, an unsatisfactory fixation and scorching of the recording sheet may occur. With a view to evading such disadvantages, it is common in practice that the temperature of the heating roller is detected and utilized for temperature adjustment to maintain the preset level always.
2. Description of the Prior Art:
In most of the hitherto known temperature control systems of the above type, a thermocouple is used as the temperature sensor for the fixing means, for example a pair of rollers as described before.
To this end, the thermocouple is disposed in physical contact with the surface of the heating roller, as the result of which injuries are often produced to the heating roller as well as the mounting elements for the thermocouple.